


The Masked Killer

by error_shy



Category: Undertale (Video Game)
Genre: M/M, Underfell Sans (Undertale), Underswap Sans (Undertale)
Language: English
Status: In-Progress
Published: 2020-04-29
Updated: 2020-04-29
Packaged: 2021-03-02 03:28:26
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 17
Words: 3,349
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23908477
Author URL: https://archiveofourown.org/users/error_shy/pseuds/error_shy
Summary: Dream and Ink flee from a battle with the gang, accidentally leaving Blue behind. After months of searching for him and not finding him, they lost hope and the star sabs was pronounced dead.Meanwhile in the distance, a masked figure with a dark cloak watches the two, waiting for its plan to unfoldA/N: I am new to AO3 and hope I got the tags correct ^^
Relationships: Sans/Sans (Undertale)
Comments: 36
Kudos: 59





	1. The Loss Of A Dear Friend

Blue watched in horror as his dear friends opened a portal. They weren't leaving him behind, right? RIGHT?! 

His thoughts were interrupted by Cross, knocking him to the ground. He watched as his friends fled through the portal. He couldn't believe it. Sadness and despair tore at his soul. It wasn't like one out of three would make a difference.

Ink cursed, looking behind himself just as the portal closed. Blue hadn't come with them. Dream looked at him. "What's wrong, Ink?" He asked, looking at the distraught creator. "Blue...... we left him there...." Ink said. Dream's eyes widened and he immediately opened a portal but Ink stopped him.

"Wait. We can't go back."

"WHAT?! HE'S OUR FRIEND INK!"

"We're just gonna get ourselves captured this way. We need to heal up and then we can look for him"

"WE DON'T HAVE TIME TO HEAL UP! BY THE TIME WE'RE HEALED, HE COULD BE DEAD!" 

"Would you rather us all be captured?!?!"

Dream was silent. It felt wrong to him, abandoning his friend like that. Ink sighed. "We'll come back for him. I promise."

Unfortunately, both you and me know that was not the case. Ink never looked for Blue no matter how many times Dream begged.

And Dream had to suffer with The Loss Of A Dear Friend.


	2. The Kindness Of The King Of Negativity

**Summary for the Chapter:**

> While the whole Multiverse is grieving Blue's death, Blue is "captured" by the gang

Blue began to sib as the portal closed behind Ink and just as he thought it was all over.... Nightmare halted the gang's attacks. He made a small 'tsk' noise and picked up the injured Blue with one of his tentacles.

Blue was surprised by the action, looking at the king of negativity in confusion. His grip was gentle and loose as if to not hurt the other. Blue was confused by his actions. Why was he helping him?

Nightmare opened a portal to a dark AU with a large, gloomy looking mansion full of fog. Blue shivered. This place looked like a cliche horror castle but slowly decaying. Nightmare and the gang stepped through, closing the portal behind them.

The inside of the mansion wasn't that bad. It actually looked quite pleasant with dark oak floor boards and light blue coloured walls. Blue was expecting to be thrown in a dirty dungeon or be tortured until he told them what they wanted to know.

But instead, Nightmare brought him to a fairly large room with a king sized bed which had light cyan covers and four soft pillows as well as a closet, a small desk and a chest in the corner. Nightmare put Blue in the bed and left. Blue could barely hear him talking to the other gang members.

"I new it.... I just didnt expect it so soon..... that starving artist is getting bolder....."

"What should we do with him?"

"Keep him here. There's no way that starving artist is gonna let him back without starting a whole shitstorm."

"If he lets him back anyway"

"Yeah."

The voices faded away, leaving a confused Blue

**Notes for the Chapter:**

> I was reluctant to post this chapter since its involved with the plot twist of the story but I decided "to help with it"
> 
> Hope you enjoyed


	3. An Old Friend, A New Identity

**Summary for the Chapter:**

> Error comes to visit Blue with a gift that will change his life forever.

It had been about a week since he was brought to the gang's hideout. He was surprised by the way they treated him. Instead 9f treating him like a prisoner, they treated him as an equal. He would cook with Horror, spar with Dust, carve with Killer and even read with Nightmare. 

The gang always showed him the versions of themselves the Multiverse decided to ignore. The part of themselves that made them sanses. Blue was actually happy in the castle and had permission to roam around as he pleased. 

One day, while Blue was in his room, there was a knock at the door. "Come in!" Blue said cheerfully. The door slowly opened to reveal Error who was holding a large box in his hands. Blue was ecstatic to say the least. He hugged his best friends so tightly his arms hurt. After Error managed to get Blue off him, they both sat on the bed.

"Its so nice to see you! Where have you been?"

"I had quite a bit of work to do before I could take a break. Ink is in his creative mood. He even took a Swap Sans from a different AU to take your place...."

"Oh....... how did Papyrus react?"

"He doesn't know. Ink created a copy of you and put him in your place...."

".......so I was replaced?....."

"........yes........ but I've got something to help you"

He opened the box to reveal a dull light blue shirt with black pants and a navy cloak as well as a white mask with only eye holes which seemed to be made out of clay. Blue looked at the box in awe.

"With this, no one will recognize you and you can join the gang........ you can get revenge......"

"Heh......... and I always thought I'd end up as a hero.........."


	4. The New Threat

**Summary for the Chapter:**

> Ink, Dream and Swap are fighting the gang when a new threat appears

Dream frowned as he dodged another bone attack. This wasn't good. The gang had always outnumbered them but this time, they seemed more hostile. Even Cross summoned two large knives instead of one this time.

Swap was having a slightly hard time keeping up with Killer's attacks. It was hard fighting an enemy for the first time since you don't know their attacks and their patterns. 

Ink himself was fighting Dust, trying his best to keep an eye on his team. Nevertheless, they were fighting a losing battle. And things were only about to get worse for the star sanses.

Swap had just managed to restrain Killer when all of a sudden, he was struck in the back of the head. Everyone looked up to see a figure wearing a long navy cloak and black pants with a mask that only had small eye holes. Swap looked up at the figure in fear as it stared at him with wide crazed eye lights.

The gang seemed amused by the figure, knowing who hid behind the mask. The masked figure grabbed Swap by the scarf, piercing his head with a bone.

Dream screamed and Ink looked away. Swap fell to his knees, slowly beginning to dust. Ink mentally cursed. This wasn't going as planned. He grabbed Dream's arm and fled, ignoring the other's screams and sobs.

The figure looked up at the gang, bloody bone in hand. 

"You know......... I should have joined eons ago"


	5. Telling The News

**Summary for the Chapter:**

> Papyrus looses his beloved brother.

**Notes for the Chapter:**

> This chapter is a bit short. I hope you don't mind ^^

"He didnt make it........ a masked figure attacked him. We tried to save him and even fought the masked man but Nightmare and his gang knocked us out and when we woke up, he was long dead."

Dream didnt even bother correcting the creator's story as he watched Papyrus' face turn from confusion to shock and grief. He began to sob and after a minute or two, headed to the bar to drink off his sorrows.

"For how long are you going to keep lying to people?"

"As long as I need for my plan to work. Just trust me and you will get your AU and brother back"

Dream was silent. He knew Ink was his only hope of seeing Nightmare and the village again so he silently did as told. One of these days. Just one of these days, he could go home. 

But then again...... who was he trusting?


	6. Rumours About The Mask

**Summary for the Chapter:**

> Ink is keen on spreading rumours of the masked man so the other sanses will not even hesitate to help him in battle

"Did you hear about Masked Sans?"

"I heard he tortured the people of his AU and starved them off"

"Really? I thought he skinned them alive"

"These freaks just keep comin' don't they?"

"Wish I could kick his ass!"

"I've once seen him stalking a Swap Sans"

"Of course the sicko is going for Swap... they always do...."

"I swear to Asgore if he doesn't get caught soon, I'm gonna kill him myself!"

"Now now Red, you know we can't take risks like these just yet...."

"Besides, I heard the dude ate his own Papyrus"

"Disgusting"

Little did they know the person they were so disgusted of was just sweet little Blueberry 


	7. Happy Bitty Birthday

**Summary for the Chapter:**

> Blue takes Error to adopt a Bitty for his birthday

Blue smiled excitedly as he led the blindfolded destroyer to the bitty adoption center. The gang and himself had been planning this for months, so this would be the best birthday Error ever had. He slowly led Error inside and took off his blindfold. Error gasped and smiled, looking around. He had visited the cities before and was excited to revisit them. Blue and Error walked over to Mama Cry. "Hello and welcome to the bitty adoption center. Would you like to adopt?" "No we're just here to visi-" "actually, we are," Blue said. Error looked taken aback. What? He was getting a bitty??? Excitement washed over the destroyed as they were led to the bitty pen to pick out a bitty. As soon as Error entered the pen, bitties ran over to greet him. The bitties all loved Error.

Little voices greeted him happily and Error smiled back at them. He began talking to the bitties, thinking of who to bring. Nightmare had told Blue the max number of bitties was four since Error would obviously try to adopt the whole adoption center. Error felt quite guilty for not being able to take all the bitties. Many bitties were begging Error to adopt them after hearing he wasn't just visiting. Even a few Edgys swallowed their pride. Error didn't know what to do. He eventually settled on a sad-looking Sansy bitty, a clingy Edgy bitty, a crying Runt/Cherry bitty, and a half-asleep soft bones bitty.

The Edgy bitty (6 inches) had crawled into Error's hood and refused to leave unless adopted, the Sansy bitty (5 inches) had used his best attempt at puppy dog eyes to guilt trip Error into adopting him, Error didn't have the heart to say no to a Cherry bitty (4 inches) and the Soft Bones bitty (3 inches) looked too adorable not to take. All the other bitties looked a bit disappointed but Error promised to visit them as often he could, which left them hopeful. After filling out some paperwork while talking to his new bitties, Error and Blue returned to the castle. Error was honestly not expecting any more surprises for the day but as soon as he stepped into the kitchen, he was met with a simple cake of his favorite chocolate, his favorite snack, and the gang ready for a movie night to celebrate his birthday. They knew Error liked simple parties where he got to spend time with his friends and his friends only.

After being almost brought to tears and sitting in the comfy pillow and blanket throne the gang made on the couch, they began watching a movie. Error gave his bitties some popcorn, all except Soft Bones who was sleeping and began planning out in his head what clothes to make for each. This was definitely the best birthday he ever had, spending it with friends, bitties, and most importantly, snacks!


	8. Giving the Bitties Names

**Summary for the Chapter:**

> just a mini-chapter to introduce the bitties

"So... what should I name you?" "I just don't want a dumb name," Edgy said, crossing his arms. "Meh. I dunno" the Sansy said. ".........i.....I want a......p-pretty name....." The Cherry mumbled. "I dunno......." the Soft Bones said, yawning. Error though for a while before pointing at the edgy. "You're Rooi" He pointed at the Sansy "You're Sonny" He pointed at Cherry. "You're Coretta" And finally, he pointed at Soft Bones. "And you're Sammon" Error finished, smiling. The bitties look at each other before smiling. Rooi seemed to like his name, Sonny didn't seem to mind, Coretta had a small smile and Sammon was already asleep again.


	9. Master Chef with Horror Sans

**Summary for the Chapter:**

> Horror isn't a picky eater but he is a picky cook. 
> 
> Even Gordon Ramsey quivers before him

**Notes for the Chapter:**

> Making 6 short chapters to show Blue's relationship with the gang.

"Not enough flavour"

"Too spicy"

"Not enough salt"

"Too humid"

"Too dry"

"Too undercooked"

"Too crunchy"

"Not enough lettuce"

"Too much meat-" 

"Horror, it's a taco. Not a gourmet meal" Blue reminded the other, laughing a little. Horror was very anxious of what people thought of his cooking so he cooked everything to exact perfection. "But-" "Horror, it's a TACO. A taco usually has a lot of meat inside." Blue reminded the other again. Horror looked uncertain but let it slide. They put the tacos in the oven and turned on a timer. "So, Mr. Ramsai, did I pass onto the next round of Masterchef?" Blue asked, jokingly. Horror smiled back. "Nope!"


	10. A Battle well won and a cunning plan

**Summary for the Chapter:**

> Ink comes up with a plan that might ruin everything for the gang

"We will split up into fours teams. The front liners, The back liners, The ambushers and Dream and I. The ambushers will consist of Outer, Classic and G. Outer, being in the neutral side, will be able to befriend the gang and persuade them into coming to the ambush spot. Classic will make a bone cage, trapping the gang inside while G summons an anti magic barrier around them. This way they can't teleport out. The front liners, consisting of Fell, Geno, Reaper, Fresh, Stretch and Edge, will attack the gang members from outside the cage while the front liners, consisting of Sci, Lust, Cloud, and Swapfell, will distract the gang from the cliffs above, making them look up. At that moment, Dream will shoot Nightmare's eye from above the cliff, blinding him, while I dump red paint all over them. Nightmare will be disoriented and without their boss to guide them, the gang will be confused. Then, I splash them with purple paint, chaining them up. 

All in favour of the plan raise your hands"

All hands went up except for Dream's.


	11. Such a gullible glitch

**Summary for the Chapter:**

> Outer approaches Error in Outertale. To his surprise, the destroyer is more gullible than he seems

* * *

Outer took a deep breath as he watched the destroyer from the thick treeline. The whole Multiverse depended on him for this plan to work. He needed it to work. As silently as possible, he approached the destroyer, careful not to make a sound. He could hear three little voices talking to the destroyer. As he got closer, he saw four bitties. One in the Destroyer's hood, sleeping. One biting the Destroyer's sleeve. One on the Destroyer's shoulder, looking like they were about to cry and one watching what the destroyer was doing. 'Poor bitties...' Outer thought. The bitty on Error's shoulder, most likely a cherry, saw him and quickly pointed him out to Error, who turned to face him.

He froze in fear as the destroyer looked at him. Then, with a small smile, patted the ground next to him. After about a minute, Outer reluctantly sat next to him. He could see the destroyer was sewing a corsetted dress the size of the bitties. The dress' top part was light pink with black sleeves, a vibrant hot pink corset and a slightly goofy black skirt. Set aside were two black leather boots and beside the destroyer was a sketchbook with clothing patterns and a picnic basket full of sewing supplies and fabric.

For the first few minutes, Outer just watched in awe as the destroyer made the tiny dress, adding a few ruffles here and there. After it was done, he gently held the bitty on his shoulder, set it down and handed it the dress. "T-Thank you..." the cherry said shyly before hiding in a Bush to change. ".......where did you steal then from?" Outer asked. "I dIdN't StEaL tHeM. i AdOpTeD tHeM." Outer looked astonished at this fact but then began to question how truthful it was. "Suuuure......"

Error began making clothes for the Edgy who was still chewing his sleeve. He made him a red sweater with a large leather overcoat and even managed to make a small yellow belt and shoes "so..... umm.... why are you making them clothes instead of just buying them?" Outer asked curiously. "i'M nOt ReAlLy AbLe To Be SeEn In PuBlIc FoR tOo LoNg WiThOuT iNk ShOwInG uP' Error admitted, handing the clothes to the Edgy just as the Cherry returned. 

Outer was confused. Why wasn't the destroyer attacking him? Why was he not even in the least wary of him?

Was he really that naive and gullible?


	12. Quick Vote Chapter!

* * *

This story was originally supposed to be Errorberry but I'll let you pick one from the following ships:

Ships with Error:

Errorberry

Errorouter

Errormare

Ships with Blue

Errorberry 

Dustberry

Dreamberry

Ships with Dream 

Dreamberry

Drink

Kream 

Those are the onpyships that may appear in this book. 

You can vote for three max

Comment your vote and the ship with most votes win

Errorberry: III

Errorouter: I

Kream: II


	13. Announcement

So in the firing chapter, the winners were Errorberry, Kream and Errorouter.

I don't know how the hell to fit two ships with Error into this but screw it! Errorouterberry! Boom!


	14. A peculiar friend

**Summary for the Chapter:**

> Outer befriends Error after only a few days. But unfortunately for him, "Masked Sans" is not so easily fooled by his facade.

**Notes for the Chapter:**

> Sorry this is bad. It was rushed since AO3 refreshed 3 times, deleting all my progress qwq

When Blue first heard Outer had befriended Error, he was having none of it. Outer would always speak badly about Error and all of a sudden he had a change of heart? Blue wasn't a naive little kid anymore. He had learned. After his friends abandoned, he had learned. After his brother had replaced him, he had learned. After he got his first kill, he had learned. 

But Error never learned. He always held onto the hope one day the creator would give up creating and he could live a normal life. But Blue knew that would never happen. And he wasn't going to let anyone take advantage of Error's naive nature.

So one day, he decided to follow Error to Outertale to have a little chat with Outer. With his mask and cloak on, he was unrecognisable as the sweet little Blueberry he used to be. He had gotten taller, even though he was still not very tall compared to the gang, and he had gotten more ruthless. He no longer showed mercy. Only wrath.

As soon as Outer saw the masked sans he froze. He was dreading this day. The day Error's fellow gang members followed him. Masked sans was quiet for most of their chat. Just as Error started packing his things, Masked Sans pulled him into a corner. He took off his mask and stared at him right in the eyes. Outer would have gone pale if he could. 

"........you're not ruining him like Ink ruined me"


	15. Dream's role

**Summary for the Chapter:**

> Dream is given a task for after the plan

* * *

"IM NOT GONNA DO THAT! ARE YOU INSANE?!?!"

"You have to, Dream. For the Multiverse"

"SCREW THE MULTIVERSE, IM NOT KILLING MY BROTHER!"

"You have to."

"IM NOT GONNA DO IT!"

"Dream."

"NO! YOU PROMISED ME MY AU BACK! NIGHTMARE IS PART OF THAT!"

"I'll make a copy of him."

"THATS NOT THE SAME! IM NOT REPLACING MY BROTHER! NOR AM I GOING TO KILL HIM!"

Outer watched as Dream stormed out of the room, tears clear in his eyes. 

This was a mess


	16. A/N

* * *

Sorry for not updating recently

I am having a bit of a writer's block at the moment


	17. A chance

**Summary for the Chapter:**

> Oh what's this? I'm alive? Well yes I finally came out of writers block and I've got some new ideas for this story

Outer had learned many things about Error in their time together. Like how Error liked to see and make dolls and make clothing, or how oblivious Error really was, and his lack of knowledge of simple things like food names. He might aswell have been talking to a completely different person than the destroyer of worlds himself. He thought Error might have a twin or a double personality but both those options werent very likely. Most unnerving was the presence just in the corner of his eyes. That mask which had revealed things he wished he could unsee. He would never forgive himself for helping spread all those lies about Blue without even knowing. He would never forgive himself for informing Ink whenever Error was in Outertale. And he knew he would never forgive himself after luring them into Ink's trap.

He even got to know the gang more, see the side of them they hid from the world. See what they are when not in battle. He needed to pinch himself to make sure he wasn't hallucinating. He was taken aback by them having hobbies, interests, personalities other than psychotic. Had he really misjudged them that badly? That was made apparent after his cooking sessions with Horror, DIY projects with Cross, geeking out about books with Nightmare and stargazing with Dust. It felt so complicated. It felt like he was blinded by the creator's words. Afterall, Ink WAS soulless.... he wouldn't feel any remorse demonising them. He even did it to his own friend. But then again, Nightmare and his gang HAD done terrible things. But why? What was their motive?

Well Outer only had 20 days before the plan. 

20 days to convince the others to ditch it.

**Author's Note:**

> Thank you for reading! 
> 
> I hope you enjoyed this chapter
> 
> Have a wonderful day!


End file.
